The overall purpose of the Cell and Tissue Biology Core is to offer specialized services and reagents to Center members that are not readily available in their individual laboratories. Techniques such as primary liver cell culture and liver perfusion are complex and expensive; they cannot be performed without a very substantial investment in equipment and personnel training. Moreover, 20 years of experience have shown clearly that success is operator-dependent. Laboratories that perform these procedures on an occasional basis only are unlikely to achieve reproducible results. For example, when cell isolates are being prepared on a daily basis, as in the Core, small changes in quality are; readily detected and appropriate analysis is done. This is particularly important when new batches of reagents are introduced that may differ in key properties from those in current use. In this case, careful parallel testing is done to ensure that quality is maintained. Also, reagents such as enzymes for tissue dissociation have a limited shelf life. This is not an issue for a busy Core operation but can be important for the individual laboratory that performs the procedure on an occasional basis only. Thus, centralization of these services within a Core permits: (a) technology transfer to a broad range of Center investigators; (b) standardization of techniques with rigorous quality control; and (c) economy of scale. All of these enhance the productivity and efficiency of the Center as a whole. Another important mission of the Cell and Tissue Biology Core is to improve on existing techniques and develop new services as required by Center members. The history in this regard is noteworthy, as described above, and this remains a fundamental part of the Core?s mission and its service to Center investigators.